A three-way catalyst device coupled to the exhaust of a combustion engine reduces combustion by-products such as carbon monoxide, hydrocarbons, and oxides of nitrogen. However, as the catalyst device ages, its ability to store oxygen diminishes leading to a decrease in efficiency. In order to determine the efficiency of the catalyst device, systems monitor the ability of the device to store oxygen.
One approach to monitor catalyst performance includes running a catalyst monitor following deceleration fuel shut-off (DFSO) events, as such operation may provide an advantageous condition for monitoring the efficiency of the catalysts in an emission control device. In particular, running the monitoring routine following DFSO reduces the need to operate the engine in a lean combustion mode in order to saturate the catalyst. Further, during DFSO no fuel is injected while the engine rotates and pumps air through the catalyst, thus catalytic saturation may occur faster and more completely than during lean engine operation, with reduced risks from oversaturation.
However, the inventors herein have also recognized that such an approach can have problems in providing accurate information when applied to a range of vehicles with different lengths between the catalyst and the engine. For example, the point from which to start summing the amount of rich reactants provided to the catalyst may not be well correlated with the resumption of fuel injection.
One example approach to address the above issue may include a method is provided for monitoring an emission device coupled to an engine. The method comprises: following a deceleration fuel shut-off duration, indicating degradation of the emission device based on an a total amount of rich products required to cause a downstream switching sensor to become richer than a threshold, summing of the total amount started when the downstream sensor begins to drift away from a lean reading. For example, the amount of rich products required to cause a sensor to become richer than a threshold may be correlated to an amount of oxygen stored in the emission device more accurately by starting the summation (e.g., integration) of those products at the right condition. In this way, even as the distance between the catalyst and the engine may vary from one vehicle model to the next, delay errors that would otherwise be introduced may be reduced. This is particularly true with respect to vehicle up-fitters, such as in the example limousines, where a significant variation in the length can be introduced for different applications of a given emission system.
Further, the inventors have recognized that even though the downstream sensor is furthest downstream, its initial drift away from the lean value provides the most accurate indication of when the rich reactants actually reach the catalyst. Thus, although it is counter intuitive to use the most downstream sensor to start the integration (as conventional thinking is that it would have the largest delay), such an approach actually improves repeatability in the estimation results. Further, it removes errors introduced in any attempts to rely on the upstream sensor to start the summation, since the upstream sensor may have a relatively delayed reaction to the rich reactants.
Thus the indication of degradation of the emission device may be based on the amount of stored oxygen. The indication of emission device degradation may be further based on air mass and temperature during delivery of the required rich products to account for effects of such parameters on the indication of degradation.
In such an approach, the oxygen storage capacity may be identified via an integrated fuel metric. Furthermore, since little to no combustion occurs during DFSO when the catalysts are being saturated, the negative effects of catalyst oversaturation may be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.